Pfizer Sell-Off on Breast Cancer Drug News Unwarranted

The cheapest drug maker in the S&P 500 just got cheaper amid debate over early study results for a promising new breast cancer drug.

When are good clinical trial results good enough? Pfizer investors are learning the answer the hard way.

Early-stage study data unveiled Sunday at the annual meeting of the American Association for Cancer Research in San Diego, showed that Pfizer's (ticker: PFE) experimental breast cancer drug palbociclib nearly doubled the amount of time breast cancer patients lived without the disease getting worse.